Difference Between UTR and Intron

The key difference between UTR and intron is that UTR is a non-coding nucleotide sequence which is included in the mature mRNA sequence while intron is a sequence that is not included in the mature mRNA molecule.

UTR or untranslated region is a non-coding sequence which is found in the mRNA molecule. In each side of the mRNA sequence, we can see one UTR. Therefore, there are two UTRs as 5’UTR and 3’UTR. In contrast, an intron is a non-coding sequence which is found in between exons of the gene. Introns are spliced off when making mRNA. Hence, introns are not seen in the mRNA sequence. However, both UTR and intron are important elements of eukaryotic genomes.

CONTENTS

1. Overview and Key Difference
2. What is UTR 
3. What is an Intron
4. Similarities Between UTR and Intron
5. Side by Side Comparison – UTR vs Intron in Tabular Form
6. Summary

What is UTR?

UTR or untranslated region is a sequence that is present on each side of the mRNA sequence. Therefore, there are two UTRs. One is present on the 5’ side, and it is known as 5’UTR while the other is found on the 3’ side and it is known as 3’UTR. 5’UTR is also known as a leader sequence, while 3’UTR is known as a trailer sequence. Structurally, 5′ UTR is found upstream to the coding sequence while 3′ UTR is found immediately following the translation stop codon. Furthermore, the base composition of the 5’UTR differs from the base sequence of 3’ UTR. Generally, the G+C content of 5′ UTR sequence is greater than that of 3′ UTR sequence. When the mRNA sequence is translated into an amino acid sequence, these two UTRs remain untranslated.

Untranslated regions play a crucial role in post-transcriptional regulation of gene expression. They participate in controlling translation, degradation, and localization of mRNA (transport of mRNAs out of the nucleus). Moreover, UTRs are responsible for the stability of mRNA and translation efficiency.

What is an Intron?

Introns are the nucleotide sequences of a gene which do not code for proteins. Hence, they are termed as non-coding sequences. They are located between exons. Introns, together with exons, transcribe into pre mRNA molecule. However, since they are not involved with the genetic code of the protein, they are excluded from the RNA molecule through a process called RNA splicing. The remaining RNA sequence is known as mRNA or the mature mRNA molecule.  Therefore, the mRNA molecule does not contain sequences of introns. RNA splicing occurs in two ways as cis-splicing and trans-splicing. Cis-splicing occurs when a single intron is present in a gene. Trans-splicing occurs when there are two or more introns within a gene.

These sequences can be seen in both DNA and RNA. Hence, the term intron could be used to refer to both non-coding sequences of DNA and RNA. It is important to notice that ribosomal RNA (rRNA) and transfer RNA (tRNA) also contain genes with introns. But similar to DNA transcription, when rRNA and tRNA genes transcribe, these non-coding sequences are excluded from the final RNA molecule. Therefore, these are called untranslated sequences of DNA.

The immediate function of introns is a little unclear, but it is believed that these are important to constitute for a diversified, yet related proteins from a single gene. Intron-mediated enhancing of gene expression has been accepted as another important function of them.

What are the Similarities Between UTR and Intron?

• UTR and intron are non-coding nucleotide sequences which do not translate.
• Both are included in the gene structure.

What is the Difference Between UTR and Intron?

UTR or untranslated region is a nucleotide sequence found on each side of the mature mRNA molecule. Meanwhile, the intron is a non-coding sequence found within the gene between exons. So, this is the key difference between UTR and intron. UTRs are not spliced off while introns are spliced off. Therefore, introns are not considered as untranslated regions. UTRs are involved in the post-transcriptional regulation of gene expression while introns have no importance in post-transcriptional regulation of gene expression.

Below infographic tabulates more differences between UTR and intron.

Summary – UTR vs Intron

UTR and intron are two types of non-coding sequences. But intron is not included in the mature mRNA sequence since introns are spliced off by the RNA splicing mechanism. UTRs are included in the mRNA sequence. Thus, this is the key difference between UTR and intron. Functionally, UTRs are important in the post-transcriptional regulation of the gene expression, while introns are not important in that process.

Reference:

1. “Intron / Introns | Learn Science At Scitable”. Nature.Com, 2020, Available here.
2. “Untranslated Region”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “MRNA structure” By Daylite – Own work (Public Domain) via Commons Wikimedia
2. “DNA exons introns” By National Human Genome Research Institute – (Public Domain) via Commons Wikimedia